ABSTRACT
The clustered organization of most imprinted genes in mammals suggests coordinated genetic and epigenetic control mechanisms. Comparisons between human and mouse will help in elucidating these mechanisms by identifying structural and functional similarities. Previously we reported on such a comparison in the central part of the mouse imprinting cluster on distal chromosome 7 with the homologous Beckwith-Wiedemann syndrome (BWS) gene cluster on human chromosome 11p15.5. Here we focus on the adjacent sequences of 0.5 Mb including the KCNQ1/Kcnq1 and CDKN1C/Cdkn1c genes, which are implicated in BWS, and on one of the proposed boundary regions of the imprinting cluster. As in the previously analysed central region, this part of the cluster exhibits a highly conserved arrangement and structure of genes. The most striking similarity is found in the 3' part of the KCNQ1/Kcnq1 genes in large stretches of mostly non-coding sequences. The conserved region includes the recently identified KCNQ1OT1/Kcnq1ot1 antisense transcripts, flanked by a strikingly conserved cluster of LINE/Line elements and a CpG island which we show to carry a maternal germline methylation imprint. This region is likely to be the proposed second imprinting centre (IC2) in the BWS cluster. We also identified several novel genes inside and outside the previously proposed boundaries of the imprinting cluster. One of the genes outside the cluster, Obph1, is imprinted in mouse placenta indicating that at least in extra-embryonic tissues the imprinting cluster extends into a larger domain.
Subject(s)
Beckwith-Wiedemann Syndrome/genetics , Genomic Imprinting/genetics , Potassium Channels, Voltage-Gated , Alternative Splicing/genetics , Amino Acid Sequence , Animals , Chromosomes, Artificial, Bacterial/genetics , Chromosomes, Human, Pair 11/genetics , Cloning, Molecular , Conserved Sequence/genetics , CpG Islands/genetics , Cyclin-Dependent Kinase Inhibitor p57 , Exons/genetics , Expressed Sequence Tags , Female , Germ Cells/metabolism , Humans , Introns/genetics , KCNQ Potassium Channels , KCNQ1 Potassium Channel , Long Interspersed Nucleotide Elements/genetics , Mice , Molecular Sequence Data , Multigene Family/genetics , Nuclear Proteins/genetics , Placenta/metabolism , Potassium Channels/genetics , Receptors, Steroid/chemistry , Receptors, Steroid/genetics , Receptors, Tumor Necrosis Factor/chemistry , Receptors, Tumor Necrosis Factor/genetics , Sequence Alignment , Sequence Analysis, DNA , Sulfates/metabolismABSTRACT
In human and mouse most imprinted genes are arranged in chromosomal clusters. This linked organization suggests coordinated mechanisms controlling imprinted expression. We have sequenced 250 kb in the centre of the mouse imprinting cluster on distal chromosome 7 and compared it with the orthologous Beckwith-Wiedemann gene cluster on human chromosome 11p15.5. This first comparative imprinting cluster analysis revealed a high structural and functional conservation of the six orthologous genes identified. However, several striking differences were also discovered. First, compared with the mouse the human sequence is approximately 40% longer, mostly due to insertions of two large repetitive clusters. One of these clusters encompasses an additional gene coding for a homologue of the ribosomal protein L26. Second, pronounced blocks of unique direct repeats characteristic of imprinted genes were only found in the human sequence. Third, two of the orthologous gene pairs Tssc4/TSSC4 and Ltrpc5/LTRPC5 showed apparent differences in imprinting between human and mouse, whereas others like Tssc6/TSSC6 were not imprinted in either organism. Together these results suggest a significant functional and structural variability in the centre of the imprinting cluster. Some genes escape imprinting in both organisms whereas others exhibit tissue- and species-specific imprinting. Hence the control of imprinting in the cluster appears to be a highly dynamic process under fast evolutionary adaptation. Intriguingly, whereas imprinted genes within the cluster contain CpG islands the non-imprinted Ltrpc5 and Tssc6/TSSC6 do not. This and additional comparisons with other imprinted and non-imprinted regions suggest that CpG islands are key features of imprinted domains.
Subject(s)
Beckwith-Wiedemann Syndrome/genetics , Conserved Sequence , Genes, Tumor Suppressor , Genetic Variation , Genomic Imprinting , Membrane Proteins , Multigene Family , Tumor Suppressor Proteins , Amino Acid Sequence , Animals , Base Sequence , CpG Islands , DNA, Complementary , Humans , Mice , Molecular Sequence Data , Proteins/genetics , TetraspaninsABSTRACT
Domina (Dom) is a novel member of the FKH/WH transcription factor gene family of Drosophila. Two alternatively polyadenylated Dom transcripts of 2.9 and 3.9 kb encode a 719-amino-acid protein with a FKH/WH domain and a putative acidic transactivation domain. Dom is mainly expressed in the central and peripheral nervous system. Homozygous mutants show rough eyes, irregular arrangement of bristles, extended wings, defective posterior wing margins, and a severely diminished vitality and fertility. Heterozygous Dom flies are morphologically wild type but show suppression of position-effect variegation. Consistently with this chromatin effect DOM protein is accumulated in the chromocenter and, as expected from a transcription factor, is found at specific euchromatic loci. Sequence comparison suggests that DOM of Drosophila is homologous to the chordate WHN proteins. The chromatin modifying capability of DOM is probably based on the FKH/WH domain, which shows a remarkable structural similarity to the winged-helix structures of H1 and the central globular domain of H5.
